Object Oriented Apologetics

Object Oriented Apologetics
Vance Lucas
CodeWorks 2009 Dallas
September 27, 2009

What?
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Not an apology
Greek root
- apologia (απολογία)
- “speaking in defense”
To defend the use of, and
provide rational reasoning for

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Who is it for?
For People Who:
Are “on the fence” about OOP vs procedural
Are unconvinced of the usefulness of OOP
Want to learn WHY they should learn about OOP

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Purpose: To Get You Hooked on OOP

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NO Academic or Mundane Examples

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No Shapes, Cars, Fruit, or Bicycles

<?phpclass myClass { public function myClass(){ } public function echoMe(){ echo 'me'; } } $mine=new myClass(); $mine->echoMe();
?>
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No “Hello World” Scripts

So… Why OOP?

Polymorphism
I nheritance
E ncapsulation
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Polymorphism

Making things that are not the same look the same
Relies on a defined interface
Inheritance is probably the most used method
The ability of type A to be used like type B
Think: Interchangeable types or components
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Polymorphism

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Real World: Different Implementations

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Procedural - Inline

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Object-oriented – Polymorphic Interface

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Inheritance

Extend from a parent class
“is-a” relationship
Creates hierarchal relationship
Get functionality for free
Global changes are easier
Inherits all functions and properties from parent
Think: A is a B, with a few differences
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Inheritance

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Controller: Zend Framework

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Model: phpDataMapper

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Warning: Keep Hierarchy Shallow

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Encapsulation

Hide specific implementation details
Reveal only methods and properties required to interact with the object
Limits interdependencies between components
Think: Separation of responsibilities
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Encapsulation

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Payment Interface – Exposed Methods

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Planetoids (by Micah Jones)

Asteroids responsible for their own movement
Different: velocities, sizes, shapes, rotations, color, and fragment pieces
All the code and math calculations for movement are encapsulated behind ‘move()’
Allows different types of objects and asteroids to be treated the same in code – “polymorphically”

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Planetoids: Code Abstraction

Other OOP-Only Features?
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Lazy-Loading

Uses __get() “magic” method in PHP5 object model
Also uses SPL interfaces to fire query on:
count()
foreach()
Used as a hook to retrieve related rows on call
Caches results so only 1 query is fired
Can eliminate N+1 query problem by mapping
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Lazy-Loading: OOP Only

Classes are actually custom types
Can type-hint for classes or interfaces
PHP Standard types:
string, int, float, boolean, array, object, null
resource
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Custom Type Creation & Type-Hinting

Other Reasons TO Use OOP?

Easily group related properties/data
Avoid using globals or passing/returning arrays
Suppress errors ala ‘undefined index’
More?
Convenience (a.k.a. Laziness)
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Request object: Why not $_POST?
Data comes from multiple sources
POST/GET, XML, JSON, etc.
Other functions
isAjax(), isPost(), etc.
Sanitizing user input
Session object: Why not $_SESSION?
More options for saving/storing
Database, separate server, memcached, etc.
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Request / Session Objects

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Request Object: Convenience, too!

Need an Example?

E-commerce Cart: Work Scope

Basic categories (1-level)
Simple products, no options, stock, etc.
Simple checkout, no user accounts
Authorize.net integration
UPS rate quotes
Admin backend
Order fulfillment
Invoice/packing slip printing

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Simple Cart

Simple Checkout
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Simple UPS Integration

So far it’s OK
It works
We finished and worked quickly
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Status Check

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Client Message
I talked to my next door neighbor’s cousin’s brother’s niece yesterday, and he says all the serious online stores have regular sales. That’s something I can do too, right?
- Bob

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Product Sales

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New Code for Product Sale

We also have to add this code to the admin backend for customer invoices.
And to the email reciepts
Sin of code duplication
Code smell
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Thoughts

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Client Message
Hey,I was at the grocery store yesterday and my daughter got 2 candy bars for $1, when they were originally $0.75 each.
I know that if I am able to do this, I’ll get a lot of sales and it will make me rich. I need to be able to do this.
- Bob

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Multi-Quantity Discounts

New Code, Again
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We also have to add this code to the admin backend and other places again.
Sin of code duplication
We could use procedural functions for this
Where would we put them?
What responsibilities do they have?
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Thoughts

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What about the future?

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Employee Discounts

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Switching to FedEx

Stock Checking
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Clearly, as the project grows, it will become a
maintenance nightmare if we continue on the
current path.
We don’t want our code to be the running joke of
the PHP community.
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We need something better

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Use the right tool for the right job

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OOP: Right tool for this job

Create a Cart class to store items
Encapsulate the pricing logic in an Item class
Single place to change the code
Item is responsible for knowing it’s price (?)
What does this imply?
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Thoughts

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Possible Code Changes

Still storing cart in session, but now we can change it later when we need to scale
Cart gets item price so it can check quantities
Cart is responsible for knowing other items in cart
Better separation of responsibility
It’s not the job of the display logic to calculate the item’s price or apply discounts
What about changing to FedEx?
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Thoughts

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Re-factor it into two classes

Package is responsible for knowing it’s own dimensions and weight
Quote is responsible for fetching a live rate quote from a carrier API service
Always think in terms of responsibility
What code is responsible for what functions?
Where does it go in my app?
Is this code doing too much?
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Thoughts

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Think about how an assembly line works

OOP Myths and Misconceptions

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Myth #1:
OOP is about code re-use

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Truth:
Re-useable code is a by-product of good OO

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Problem:
There are lots of ways to make re-useable code that are not object-oriented nor good.
It’s a bad goal.

<Code with functions and includes – re-useable>
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Functions are re-useable

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Specific implementations are re-useable

<UPS-Specific API Code>
or
<Payment Gateway-specific API Code>
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Soft interfaces are re-useable

You must set goals that will help direct you to your desired outcome
Goals narrow attention and direct efforts to goal-relevant activities, and away from perceived undesirable and goal-irrelevant actions
Re-use as a goal does not help you write good OO code. Re-use is a by-product of good OO.
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Point: Set Good Goals

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Myth #2:
Objects should always be modeled after real-world objects when possible

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Truth:
Objects should be modeled and built based on what you need to complete your task

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Problem:
Real-world object models are almost never useful in code

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Real-World Objects Change

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You are modeling things that don’t exist

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Myth #3:
Everything should be objects

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Truth:
Make objects for only what you need to. Most of the time this is data. Don’t over-complicate your code when it’s not necessary.

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Problem:
Not everything your code does can be easily represented with an object

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Application Flow
MVC diagram for
XEROX PARC 1978-79

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Programming PHP for over 10 years
Web: http://www.vancelucas.com
Twitter: @vlucas
Email: vance@vancelucas.com
GitHub: http://github.com/vlucas
Photo Set: http://www.flickr.com/photos/30728345@N05/galleries/72157622318592067/
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Vance Lucas